1. Field of the Invention
The present invention relates to a process for producing carbon black filled polyethylene resins and more particularly to a process for producing carbon black filled polyethylene resins in situ in a fluidized bed reactor.
2. Description of the Prior Art
The introduction of high activity Ziegler-Natta catalyst systems has led to the development of new polymerization processes based on gas phase reactors such as disclosed in U.S. Pat. No. 4,482,687 issued Nov. 13, 1984. These processes offer many advantages over bulk monomer slurry processes or solvent processes. They are more economical and inherently safer in that they eliminate the need to handle and recover large quantities of solvent while advantageously providing low pressure process operation.
The versatility of the gas phase fluid bed reactor has contributed to its rapid acceptance. Alpha-olefins polymers produced in this type of reactor cover a wide range of density, molecular weight distribution and melt indexes. In fact new and better products have been synthesized in gas phase reactors because of the flexibility and adaptability of the gas phase reactor to a large spectrum of operating conditions.
Polyethylene resins are particularly amenable for production in fluidized bed reactors. For many industrial applications it is beneficial, if not required, that the polyethylene resins contain carbon black. For example, products which are currently being produced with carbon black filled polyethylene resins include pipes, tubes, sheets, wire and cable constructions, and other molded or extruded polyethylene articles.
Currently, carbon black filled polyethylene resins, used for example, in black jacketing applications are generally produced by either the masterbatch or the direct addition approach. The masterbatch technique normally involves three basic steps, i.e., the preparation of the natural feedstock; the preparation of the masterbatch containing carbon black; and the blending of the natural feedstock with the masterbatch which is thereafter compounded in an intensive mixer such as a Banbury mixer, a Farrel continuous mixer (FCM) or a single or twin screw extruder.
In the direct addition technique, the natural feedstock is produced, and a blend of carbon black and the natural resin is compounded in an intensive mixer such as a Banbury or a FCM mixer.
The masterbatch technique offers a number of advantages over the direct addition technique which include good dispersion of carbon black within the resin matrix particularly with low viscosity resins.
However both of these techniques are time consuming and expensive.
It would be extremely beneficial and economically attractive if carbon black filled polyethylene resins could be produced in situ, i.e., during the fluidized bed polymerization procedure, since the costly and time consuming steps discussed above could therefore be eliminated.